1. Field of the Invention
The present invention relates generally to the field of sexually transmitted diseases and in particular to the protozoan parasite Trichomonas vaginalis. The invention also relates to the field of proteins that mediate the property of cytoadherence and to the ability of T. vaginalis parasites to attach to the human vaginal epithelial cells.
2. Description of the Related Art
The flagellated eukaryote, Trichomonas vaginalis is the etiologic agent of one of the most common sexually transmitted diseases among humans. In order to establish and maintain infection, the parasite must be able to withstand the hostile environment of the human urogenital tract. This parasite must evade immune surveillance mechanisms, such as resisting lytic antibody and complement (Alderete et al., 1987; 1991) and, equally important, overcome the constant fluid flow of the vagina. Consequently, cytoadherence by the parasite to the vaginal epithelium (Alderete and Garza, 1985; 1988a; Alderete et al., 1988b; Arroyo et al., 1992; 1993; Lehker et al., 1991) is essential for initiation and maintenance of infection and fundamental to parasite survival. The cytoadherence mechanism of T. vaginalis is complex and represents a cascade of reactions, which include a role for proteinase activity (Arroyo and Alderete, 1989) and signaling of the parasite after initial attachment (Arroyo et al., 1993).
Trichomonal cytoadherence has been shown to be ligand-receptor in nature (Alderete and Garza, 1988a; Arroyo et al., 1992; Lehker et al., 1991). Four trichomonad proteins (AP65, AP51, AP33, and AP23) have been identified as the adhesins that specifically mediate attachment to receptors on the vaginal epithelial cells (VECs) (Alderete and Garza, 1988a; Arroyo et al., 1992). That these proteins are authentic adhesins was established through fulfillment of criteria, and the relationship between levels of cytoadherence and surface expression of synthesized adhesins was established (Arroyo et al., 1992). Trichomonads expressing low levels of adhesins (Arroyo et al., 1992) have been shown to signal for enhanced synthesis of all adhesins immediately after cytoadherence (Arroyo et al., 1993). Gene expression of the four adhesins was found to be coordinately regulated at the transcriptional level by iron (Lehker et al., 1991), and such regulation may be a mechanism by which the parasite adapts to the constantly changing environment in the vagina. The adhesins are very sensitive to proteinases (Alderete and Garza, 1988; Arroyo et al., 1992) yet, paradoxically, a cysteine-proteinase activity is required for cytoadherence (Arroyo and Alderete, 1989). Finally, the adhesins appear to be immunorecessive, as evidenced by the difficulty of generating high-titered antiserum and monoclonal antibodies (mAbs) in experimental animals (Alderete and Garza, 1988; Arroyo et al., 1992; 1993; Lehker et al., 1991).
Actual numbers of female patients infected with Trichomonas vaginalis within the United States are unknown, although estimates range from 4 million to as high as 10 million. Unfortunately, fifty percent of women with trichomoniasis will not be diagnosed using the standard procedure of wet-mount detection. Alternative immunodiagnostic assays and culturing of the parasite from patient vaginal washes are ineffective or too expensive and time-consuming.
Rubino et al., 1991 have reported a 2.3 kb DNA probe isolated by HindIII digestion of total T. vaginalis DNA that recognizes T. vaginalis, Pentatrichomonas hominis and Trichomonas foetus. This probe, as reported, was still in preliminary stages of development, and the authors indicate that this probe is not suitable as a routine diagnostic tool. Thus, at the present time, no rapid, sensitive and accurate test is available for detection of T. vaginalis in human fluids, especially among individuals who represent a reservoir for this parasite because of lack of diagnosis and/or treatment. Relationships between this parasite and other STD agents, including HIV and gonorrhea, have also been established, indicating a need for increased epidemiology and surveillance among susceptible individuals. There exists, therefore, an immediate need for a method of quickly identifying patients with trichomoniasis by developing assays utilizing parasite surface proteins or nucleic acids. In addition, there is a need for preventing or controlling infection, by interfering with the adhesins mediating cytoadherence of these parasites to the vaginal epithelium.